This invention relates to an improved process for the preparation of alkyl halides from the corresponding alcohol and a hydrogen halide. More specifically, this invention relates to a process in which the conversion of the hydrogen halide is maximized in a single pass through a reactor.
The preparation of alkyl halides, particularly methyl chloride from the reaction of the corresponding alcohol with a hydrogen halide is known in the art. The by-products of the reaction are water and the corresponding dialkyl ether. Most known processes carry out the reaction with a stoichiometric excess of the hydrogen halide relative to the alcohol. As such, unreacted hydrogen halide must be discarded to the environment or recovered and recycled to the process. The recovery of the hydrogen halide, particularly hydrogen chloride (HCl) creates many processing difficulties. To begin with, HCl forms a minimum boiling azeotrope with water. Recovery and recycle of HCl is complicated by this azeotrope. Additionally, the very corrosive nature of aqueous HCl dictates that handling of this stream be held to a minimum. Finally, many known processes utilize catalysts to promote the reaction.
Steele et al., U.S. Pat. No. 3,981,938, issued Sept. 21, 1976, describes a process for producing alkyl halides by reacting the corresponding alcohol with at least a 10 mole percent excess of hydrogen halide. The reactants are passed through what Steele et al., call a "boiling bed" reactor. Under certain circumstances a "boiling bed" reactor can be considered to be a plug flow reactor. However, Steele et al., do not present sufficient information to make such a distinction. The vapors exiting the reactor are contacted with a liquid stream of alkyl halide saturated with hydrogen halide. The resulting vapor stream of alkyl halide and hydrogen halide is condensed. The alkyl halide and hydrogen halide are then separated by distillation.
Fukuda et al., Japanese Patent Publication O.P.I. 146,727/81, Published Sept. 10, 1982, describes a process in which dimethyl ether is reacted with excess hydrogen chloride in the presence of a metal compound catalyst, and wherein the unreacted hydrogen chloride and the resulting methyl chloride mixture are reacted with methanol to form additional methyl chloride. The reactor disclosed by Fukuda et al. is a column or columns packed with a solid catalyst. Fukuda et al. discloses that the reaction step in which unreacted hydrogen chloride is reacted with methanol is carried out with a stoichiometric excess of hydrogen chloride.